Instead of using the simulate jump action, make the first jump be used the same way that the second jump is used (setting Y velocity).The simulate jump action can only be done if the player is on the floor, but if you want the player to be able to jump in the air that would be a way to do it. Haven't looked at the code but I hope that helps.

@Sushin I tried that, and it did kind of work but there are some things i don't like with this. When my player does a double jump, he doers this this motion where he moves back and forth in the air, which doesn't look great. Also, my players starts going through platforms with this.

Set a variable to count the jumps. Every time player jumps add 1 to the variable.Now create a condition:On up arrow pressed and if jumpVariable<2 set y vector to -500 //this will make your character jump add 1to jumpVariable

Also add a condition for setting jumpVariable to zero when your character touches the ground